Cochlear implants provide auditory stimulation for deaf individuals through direct electrical stimulation of the auditory nerve. Electrical stimulation of the auditory nerve results in highly synchronized responses. One consequence of high neural synchrony may be a narrow dynamic range, particularly in the absence of functional cochlear hair cells, which are responsible for random, spontaneous neural activity in a normal auditory system. Rubinstein et al. (1999) proposed using high-rate electrical pulse trains to simulate spontaneous neural activity, thereby desynchronizing neural responses. High-rate pulse trains have shown evidence of desynchronizing neural responses, including recent results showing increases of the dynamic hearing ranges of cochlear implant users. The broad, long-term objective of this project is to examine the potential perceptual benefits of high-rate pulse trains for cochlear implant users, particularly those percepts related to stimulus level and the dynamic range of hearing. In the future, this information may help improve the quality of hearing and quality of life for deaf individuals with cochlear implants. The specific aims of this study are: 1) to examine the effects of high-rate pulse trains on the number of discriminable intensity steps within dynamic ranges of cochlear implant users; and 2) to investigate the potential for high-rate pulse trains to improve electrode interaction with a multi-electrode cochlear implant device. The hypotheses of the Specific Aims are, respectively, that high-rate pulse trains will increase the number of discriminable steps within the dynamic range, and that high-rate pulse trains will improve electrode discrimination. The research design and methods for this study include cochlear implant subjects with the Clarion CII device, who will be stimulated using the Clarion Research Interface (CRI-2). Specific Aim 1 will be investigated by measuring sensitivity to intensity changes (intensity discrimination) from a single electrode, and Specific Aim 2 will be examined by measuring the ability of cochlear implant users to discriminate between stimuli presented to two different electrodes. Both discrimination tasks will be measured at several stimulation levels, with and without high-rate pulse trains. The data analyses will focus on comparisons between discrimination abilities with and without high-rate pulse trains. [unreadable] [unreadable]